SUMMARY OF CURRENT RESEARCHES RELATING TO 
■102 
is visible in rudiment. The space occupied is between tbe second and 
third of Goette’s segments. 
The author regards the ear as representing a segment, and finds its 
'remote homologue in the cirrhi dorsales of Annelids. 
Fangs of the Adder.* * * § — Prof. L. Kathariner has made some interest- 
ing observations on the growth of the reserve teeth in the adder, especially 
in regard to the growth of the mucous membrane folds which brings the 
opening of the poison-duct into functional connection with each succes- 
sive fang. Anatomically the poison-duct always opens into the mouth, 
hut the sheath of mucous membrane around the base of the tooth secures 
practical, though never organic, continuity between the poison-duct and 
the canal of the tooth. Ten is the usual number of reserve fangs ; each 
seems to last about six weeks ; the separation of an old fang is effected 
by odontoclasts in the pulp-cavity. The tooth consists of cement, 
dentin, fibro-dentin, and an enarrel-cuticula, but there is no enamel. 
But the most important part of the paper is that which elucidates the 
establishment of the connection between a new fang and the poison-duct. 
Attraction-Spheres in Spermatogenesis.f — Dr. R. von Erlanger 
summarises and discusses some of the recent papers — by Niessing, 
Rawitz, Wilcox, and others — on the role of attraction -sphere and cen- 
trosome in spermatogenesis. He concludes that the centrodeutoplasm 
[= archoplasm] consists of a special substance which is not present 
in the centroplasm ( = attraction-sphere) of ova and of somatic cells. 
It collects around the centrosome when that has played its active part 
in cell-division, and it attains considerable dimensions only when the 
genital cells have passed through a long resting period. Thus there is 
ti marked contrast between the centrodeutoplasm and the centroplasm 
(van Beneden’s sphere), for the latter is formed de novo around each 
active centrosome in each division, unless, indeed, the divisions succeed 
one another very rapidly. Where a centrodeutoplasm occurs, it is dif- 
fused in the prophases of division by the fresh centroplasm ; it is scat- 
tered in the cytoplasm by the growing spindle ; it only collects again 
around the centrosome or centrosomes during the anaphases or telophases. 
Life-History of the Eel. if — Dr. C. G. J. Petersen regards the three 
so-called varieties of eel as representing three stages in development. 
The yellow eels comprise both males and females, but are all young 
fish, which have not yet commenced to assume the bridal dress of the 
adult, and in which the generative organs arc little developed. The 
frog-mouthed eels are larger females still in the same conditions ; while 
the silver eels comprise both males and females which have taken on the 
bridal dress, and are about to migrate to the sea to spawn. 
Prof. G. B. Grassi § has shown that Anguilla vulgaris , the common 
eel, matures in the depths of the sea and spawns there, that its eggs 
float, and that the young pass through a larval form known as Leplo - 
cephalus brevirosiris. 
* Zool. Jahrb., Abtii. Anat., x. (1897) pp. 55-92 (3 pis., 5 figs.). 
t Zool. Centralbl., iv. (1897) pp. 153-71. 
t Cited in Journ. Mar. Biol. Ass., iv. (1897) pp. 375-9, from ‘ Report of the 
Danish Biological Station to the Home Department,’ v. (1894). 
§ Proc. Roy. Soc , lx. No. 363, Dec. 1896. Cf. Quart. Journ. Micr. Sci., xsxix. 
.{1897) part 3 ; and Journ. Mar. Biol. Soc., iii. (1896) pp. 278-87. 
